It is known to detect and measure the current flowing in an electrical conductor by disposing a current transformer around the conductor to pick up the magnetic flux generated by the current in the conductor and, with appropriate circuitry and indicating instruments, relate that flux to a measurement of the current flowing in the conductor. Current transformers are generally large, heavy devices and are not well suited for high performance applications where light-weight, great accuracy, and reliable operation through extreme temperature changes is required. Moreover, current transformers are restricted by sensing A.C. currents.
Hall effect sensors have likewise been applied to measure current. However, they tend to be fragile devices and range limited, and are thus unsuitable in some applications. Furthermore, Hall sensors do not provide field shaping or transformer action needed to concentrate magnetic flux field for extremely sensitive contactless measurement.
Current shunts are frequently employed to measure extremely high currents. However, shunts tend to be heavy and expensive and are limited to sensing D.C. currents. Furthermore, shunts are placed in series circuit with a conductor carrying the measured current and can represent a safety hazard if they fail in an open circuit condition. Considerations of reliability and weight are particularly acute in aerospace applications where system designs frequently dictate use dozens of such devices.